Data from the Human Fertilisation and Embryology Authority, which regulates infertility treatment in the UK, shows the number of infertile men being treated has doubled in just four years.

The biggest ever study of male fertility in the developed world revealed a 59.3 per cent reduction in average sperm count between 1973 and 2011.

‘We have a huge public health problem that, until now, was under the radar. Health authorities should be concerned,’ says Dr Hagai Levine, an expert in environmental health at the Hebrew University in Jerusalem, who led the study of declining male fertility which was published in the journal Human Reproduction Update.

He says his findings should be treated as the ‘canary in the coalmine’, providing a warning for the future of male reproductive health.

Poor lifestyle is a recognised factor. As Dr Channa Jayasena, a specialist in diabetes and hormone activity based at Hammersmith Hospital in London, explains: ‘Rising obesity and diabetes are major factors in increasing rates of male infertility. This is because they damage overall fitness.

‘But, inexplicably, many affected men are apparently fit and healthy. Heavily processed foods, environmental pollution and lack of exercise may also be contributors to the problem.’